Killing X
- 
First, Hit
Ctrl+Alt+F1. - 
Then Login again
So enter your Username & Pass. - 
And Kill the Display Manager.
sudo service lightdm stop
Or:
sudo service gdm stop
But if you have a Custom display manager then look for the command to Stop it…
 - 
Finally, Go to Runlevel 3
With:sudo init 3
To test you are on Ubuntu Server Mode issue:
who -r
 
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